The objective of this project is to determine the 3-dimensional structure of the human beta2-adrenergic receptor, a G-protein coupled 7 transmembrane receptor, in the presence and absence of agonist and antagonist. Two approaches will be taken to determine the three- dimensional structure. The first approach is to determine the structure of the holo-receptor. The second approach is to truncate the receptor by removing the large soluble cytoplasmic regions of the receptor. The goal of working with the truncated molecule is to aid in the stabilization of the molecule and provide an alternative molecule for crystallization trials. The technique of electron diffraction of 2-dimensional crystals will be used. Because of the similarity in structure between bacteriorhodopsin and adrenergic receptor, the procedure used to determine the structure of bacteriorhodopsin will initially be followed.